1. Field of the Invention
The present invention relates to an image pickup device and an image capturing system that include an analog-to-digital (AD) conversion unit configured to convert a pixel signal output by a pixel into a digital signal.
2. Description of the Related Art
Image pickup devices including an AD conversion unit configured to convert a pixel signal output by a pixel into a digital signal are available. An AD conversion unit described in Japanese Patent Laid-Open No. 2011-211535 includes a reference signal supply unit. The reference signal supply unit outputs a first reference signal whose potential changes by a first amount per unit time and a second reference signal whose potential changes by a second amount per unit time, the second amount being greater than the first amount. The AD conversion unit described in Japanese Patent Laid-Open No. 2011-211535 further includes a comparison unit. The comparison unit compares a pixel signal with the first reference signal and the second reference signal. The comparison unit also compares a potential based on a noise signal with the first reference signal and the second reference signal.